1. Field of the Invention
The technical field to which the invention relates is the method and apparatus for making and projecting magnified three-dimensional images recorded via the principles of holography and/or integral photography.
2. Background of the Invention
The artistic and photographic rendering of three-dimensional images is not new. During the late nineteenth century, commercial stereoscopes became very popular toys and novelties. These devices employed the principle of stereoscopy. Most people see with two eyes. When a person opens only one eye, he sees a two-dimensional image of a life-scene from a particular from slightly different view points. When both eyes are open, the individual's mind merges the two images and acquires depth information. Therefore, both eyes are needed to enable the mind to perceive a three-dimensional scene. The principle of stereoscopy tricks a person into perceiving depth by presenting each of his eyes with separated pictures representing a given scene from slightly different view points. If the distance between the view points is approximately equal to the distance between his eyes, he will see the scene in full three-dimensions.
Over the years, a number of stereoscopic devices were invented to enable people to view three-dimensional scenes. The first scenes were reconstructed from pairs of drawings of the same scene. The two drawings were only slightly different, and were drawn as geometric projections of the same object or scene from a slightly different perspective. Eventually, stereoscopic cameras were invented that would produce photographs that would enable three-dimensional reconstruction of a photographed scene. These cameras normally have two lenses situated a distance apart equal to the interoccular separation. The camera normally takes two stereo paired photographs of the same scene with a single exposure. When these photographs are developed and viewed with an appropriate viewing device, a three-dimensional picture is perceived.
First, people were able to purchase various types of stereoscopes for viewing these pictures. Then, during the earlier part of the twentieth century, lenticular stereograms became available. These are integrated photographs (or drawings) for which no external viewing device is necessary to be able to perceive a three dimensional image. A stereogram employs a lenticular sheet comprised of small parallel cylindrical lenses. This cylindrical lenticular sheet is often called a Bonnet Screen. To prepare a stereogram, first a stereo pair of pictures are produced of the scene. These stereo pairs are exposed separately, but from slightly different angles, on a photographic film through a Bonnet Screen. After development, a viewer looking at the photograph through a Bonnet Screen sees each of the two stereo pairs reconstructed at the same angles at which they were exposed. Therefore, the two two-dimensional pictures are separated so that they are each seen by the viewer individually with each eye. Because of this, the viewer perceives a three-dimensional scene. The lenticular stereogram was the first device available wherein the stereo paired pictures were integrated into the same frame. Photographs designed for viewing with a stereoscope are individually viewable as two-dimensional pictures when the stereoscope is not in use. However, the lenticular stereogram, when viewed without the Bonnet Screen, is a very confusing picture.
Two additional processes were developed that integrated the stereo paired pictures into the same frame—the anaglyph and the vectograph. The anaglyph permitted two black-and-white stereo paired pictures to be exposed on color film—one picture being exposed using a red filter and the other exposed using a blue or green filter. When viewed with special glasses, one lens being colored red and the other colored blue (or green), a three-dimensional scene is perceived. The vectograph permitted two stereo paired pictures to be exposed on a film with an emulsion on both sides—one picture being exposed on one side of the film and the other picture being exposed on the other side of the film. The two pictures are developed such that light passing through one is polarized in one direction while light passing through the other is polarized in the other direction. This permits a viewer to use special glasses consisting of Polaroid filters to see the three-dimensional scene. Vectography has the advantage over anaglyphic photography that avoids the annoyance of seeing the red-blue tint in the scene. Anaglyphic and vectographic slides (transparencies that could be viewed in a slide projector) were widely sold. This resulted in an audience being able to view a magnified three-dimensional scene on a screen.
Eventually, anaglyphic motion pictures were displayed in theaters and ultimately on television. They were never popular as audiences found the red-blue tints very annoying. The process was refined for television to permit viewing of full color movies in three-dimensions. However, use of the red and blue glasses still produced the annoying red-blue tint. Movies employing this process were broadcast on television as late as the mid-1980's.
Vectography was never used in the cinema, but a process called “3-D” was used to produce motion pictures. This process enjoyed reasonable popularity during the 1950's. It employed a special projector with two lenses that projected each of the two stereo pairs onto an aluminized screen. Each stereo pair had a different polarity such that when a viewer used special Polaroid viewing glasses he would see a different picture with each eye. Since Polaroid filters are untinted, the 3-D movies could be viewed in full color. However, the popularity of 3-D movies eventually waned. The process is occasionally revived in present day movies, but it remains unpopular. Audiences often experienced eye strain and headaches while watching these films. They erroneously blamed this on being required to wear special glasses.
Several attempts were made to create stereoscopic motion pictures that could be viewed as three-dimensional scenes without glasses. In 1969, Dennis Gabor, inventor of the hologram, developed a process wherein a stereoscopic movie could be viewed by the unaided eye using a special screen. This process was never implemented. Had these movies been produced, the process would have required viewers to keep their heads in relatively fixed positions.
It is interesting that most people blamed the eye strain and headaches resulting from viewing 3-D movies on the glasses. One-half of all Americans wear glasses and are not bothered by them. However, the use of glasses was the only thing that appeared different to audiences, and therefore, must have caused the problem. However, the problem was actually caused by a basic problem inherent in the process of stereoscopy. When someone observes a real object, his eyes both converge and focus on the object at the same time. However, when he observes a stereo pair, his eyes converge on the apparent position of the object but focus on the screen or picture focal plane. A condition where one's eyes converge and focus at different positions is an unnatural viewing condition. The result is eye strain. All stereoscopic processes have this problem. It cannot be avoided.
Dennis Gabor invented the hologram in 1948, and in 1964, Emmet Leith and Juris Upatnicks made holography practical for the production of three-dimensional images. Holography produces three-dimensional images using a principle different from stereoscopy. In order to understand what holography is, one must first understand the concept of interference. If a small pebble is thrown into a still pool of water, waves are generated, traveling as circles away from the point of origin. A second pebble thrown into the water will generate a new set of waves. When these two waves meet, a new wave pattern is set up in the water, resulting from the interference of the two original waves. Light is also a wave-like phenomenon. Two intersecting light beams will similarly interfere to generate a resulting wave pattern. Were the two light beams to interact at the surface of a photographic plate, the interference pattern would then be photographed. Such a photograph is called an interferogram.
A hologram is a special type of interferogram. In order to produce a hologram, one of the interfering light waves must have an identifiable wavefront which can be easily reproduced or regenerated. This is called the reference beam. The second light wave is generally more complex, and is usually characteristic of the wavefront reflected from some object or scene. This is called the object beam. If, after the resulting interferogram is developed, were it to be illuminated by a wavefront identical to the reference beam, the object wavefront would be reconstructed. In other words, were a viewer to look into the direction where the object was originally, he would observe the object wavefront. He would see the object before him in three-dimensions with such reality that it would be impossible for him to determine visually whether or not the object really exists. An interferogram of this type is called a hologram. The hologram is not a photograph of the object, but rather of the interference pattern containing all the information about the object. It should be noted that no lenses need be used in making holograms. Of course, more than one object beam can be used, and all of these wavefronts will be reconstructed simultaneously by a single reference beam. Because the hologram is not a photograph of this scene, but rather a visual reconstruction of the objects in space as they existed at the time the hologram was taken, the viewer can observe the scene as he would were it to really exist. If one object blocks another, the viewer merely looks around it as he would ordinarily, and, behold, the hidden object becomes visible. Holography, therefore, provides a stark reality that no other three-dimensional process can produce.
Integral photography is a photographic technique of producing three-dimensional photographs by an integration process from many two-dimensional photographs each taken of the same object and event but at a slightly different viewing angle. In order to recreate the three-dimensional effect from all these two-dimensional photographs, a wavefront represented by the composite of all these elemental photographs is reconstructed after development, and this wavefront is similar to the wavefront produced by the three-dimensional scene itself provided that the integral photograph is viewed at a sufficient distance away. In fact, were the viewer to be positioned sufficiently far away as not to be able to resolve the individual elements in the photograph (i.e., at minimum visual acuity), he would be unable to distinguish the wavefront reconstructed from the integral photograph from that produced by the actual scene. The viewer would observe the scene in true three-dimensions. Unlike stereoscopic three-dimensionality, no special device need by worn by the viewer, and the illusion of depth of the scene in integral photography does not have to be created in the mind of the viewer; the three-dimensional images actually exist in space. A hologram is a photograph which is capable of reconstructing the same wavefront as would be created by the actual scene. In fact, were the hologram to be properly illuminated, it would not be possible for the viewer to perform any visual test to determine whether or not the objects in the scene were real. Were one to view the hologram through a small aperture, the entire scene would be visible. Moving the aperture around only changes the viewing angle. No matter how small the aperture is (within reason—limited by a size somewhat larger than the grain of the film) the entire scene would still be visible. A hologram can, then, be thought of as an integral photograph whose elemental photographs are of infinitesimal size. Therefore, an integral photograph can be though of as being equivalent to a hologram when the viewer is positioned at minimum visual acuity.
Projection of magnified three-dimensional scenes from holograms or integral photographs before large audiences has never been implemented. First, if one were to project a hologram onto a conventional screen, no image of the scene would be produced. Since a hologram is a photograph that contains information about an object and not of the object itself, a hologram projected onto a screen as a magnified photograph would not be seen as anything meaningful. On the other hand, if one were to produce a large magnified hologram so as to enable viewing before a large audience, the principles of holography dictate that the reconstructed three-dimensional image would be de-magnified. Second, there is a basic principle governing the magnification of three-dimensional images. If the three-dimensional image itself were to be magnified, the magnification in depth would be equal to the square of the lateral magnification. Such an image would not be viewable as a natural three-dimensional object. Finally, a number of engineering difficulties exist in the current state-of-the-art that have made projection of magnified three-dimensional scenes before large audiences impractical.